Torsion box and dogholes


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I'm building a new workbench for the shop and have a noob question.

I'm planning on building a torsion box for the top and will be incorporating a face vise and end vise. That part is pretty straightfortward; I'm looking at using 3/4" MDF with supports every eight inches. I'll add extra support for the vises as needed.

The issue is that I want dogholes in the top. How does one do dogholes with a mostly hollow torsion box?

One solution I see is to place 3" x 3" blocking everywhere I want a doghole. That means laying them all out ahead of time so I'd have to plan carefully now as I can't add more later on.

Alternately, I can completely replace the MDF crosspieces in the torsion box with 3" x 3" blocking.

Any suggestions?

Am I doing something silly by trying to do a torsion box with dogholes?

 

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What are you goign to use the dog holes for? If you going to use them for plane stops or just for reference and they won't see much heavy use they could be fine in the MDF top. If you are goign to use hold downs hold fasts or any sort of work holding MDF is not going to work.

Is there a reason that you want an MDF work bench? It sounds like you are putting a good investment in time and money with vise hardware. I'd recommend a wood top of some sort even if it's pine that is dried and allowed to acclimate.

I've made an MDF torsion and wood benches and for the abuse that the benches get I don't know that I'd want an MDF surface at all. When the surface of the bench gets messed up I can grab a hand plane or sander and clean it up / re flatten it. I would never recommend flattening an MDF bench as the dust from that would be miserable.

If this is an exersize in cost management, going wood doesn't have to be expensive. Constrtuction 2x10s a top would cost in the $80 range and dog holes would be a breeze. MDF would be around $100 by my guess with bracing etc, if the material was bought new. If you want to go cheap scour craig's list you may be able to score a lot of cheap wood.

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Thanks Drew.

I have a small shop and this will double as a workbench and outfeed table. My current bench is topped with MDF and it's held up ok. I treated it with paste wax and cover it with roll paper when I do big glueups so the surface has held up fairly well but after eight years, it's definitely showing its age. Given that it's lasted eight years may give you an idea how much I use it.

I was thinking MDF partly due to cost ($80 for wood for a top may be possible in the Land of Trees and Lakes but not where I live, unfortunately). Lumber from a good lumber supplier here is borderline ridiculous and frankly I've given up on wood from the local big box stores, given the terrible quality and high prices. But maybe I need to rethink that.

To answer your question, I want to get more into hand shaping, hand planing, chiseling, etc., hence the upgrade to vises, dogholes, etc. As a part time hobbyist, I'm intrigued by the idea of a torsion box and thought I'd give it a try. Is a torsion box a bad choice for such work? Is that why when I searched for "torsion box" and "dog holes", I found very little on the Net?

I could always face it with better wood when I'm done; that seems rather trivial. However, that still leaves the issue of how to even implement dogs and dogholes with a torsion box, which is basically hollow. Is that just not done?

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I believe Mike Farrington uses a MDF top torsion box as a workbench with dog holes like the MFT. I think he mostly uses those for reference pins, stop blocks, and clamps. I don’t imagine it works with holdfasts. 

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A key feature of torsion box design is that it provides a strong, flat surface while "minimizing" weight. For hand tool woodworking, this isn't a desirable feature in a workbench. The stability provided by mass will prove more suitable for hand tool operations, IMO. A thick lamination of MDF, 3 or 4 layers, will remain flat, given ordinary attention to the support structure. It will certainly be easier to construct, and dog holes can be placed anywhere you like. Don't expect them to keep their shape if used for hold-fasts, though. Even softer woods like pine or poplar give out quickly under the force applied by a traditionsl hold fast. Those screw-operated hold fasts might work fine.

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My bench top is 1.5" thick mdf. Not easy to find but it is made. It stays flat as long as it does not get wet. Varnish helps with water. Mine is 20 years old. I applied leftover varnish as it became available. Also the top is not attached. Helpful in a small shop. It is heavy enough to stay put but can be moved for a good reason.

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14 hours ago, John Nalbone said:

To answer your question, I want to get more into hand shaping, hand planing, chiseling, etc., hence the upgrade to vises, dogholes, etc. As a part time hobbyist, I'm intrigued by the idea of a torsion box and thought I'd give it a try. Is a torsion box a bad choice for such work? Is that why when I searched for "torsion box" and "dog holes", I found very little on the Net?

I could always face it with better wood when I'm done; that seems rather trivial. However, that still leaves the issue of how to even implement dogs and dogholes with a torsion box, which is basically hollow. Is that just not done?

Short of hold fasts or hold downs I don't think the torsion box would be all the limiting.

You mention a great idea. John Heitz with I Build IT recently did a work bench from plywood where he faced it with solid wood. I think that's a great way to keep cost down but also create a more durable surface than MDF provides. https://www.youtube.com/watch?v=ulZf1GTcWlk

14 hours ago, John Nalbone said:

was thinking MDF partly due to cost ($80 for wood for a top may be possible in the Land of Trees and Lakes but not where I live, unfortunately). Lumber from a good lumber supplier here is borderline ridiculous and frankly I've given up on wood from the local big box stores, given the terrible quality and high prices. But maybe I need to rethink that.

I'm not sure the region your in nor your budget but even $150 is dirt cheap in my opinion. A nice bench is worth the cost, that said I started out with a pine bench from box store garbage and still have it to this day. The bench has served me well for 5 years with no complaints. I had to re flatten it after 2 years due to the lumber drying a bit more and the top changing shape but that was no big deal. I've done the MDF torsion box thing, I'm trying to give it away currently. Being able to plunge a dog hole where i need it when i need it is way more valuable to me.

The other thing with the MDF and planning out all your dog holes ahead of time is that it doesn't really provide much room for flexibility. Shannon Rodgers with Renisance WW has a lot of good insight on dog hole position. His main advice is to not put any in a bench and drill them as you find that you need them where yo need them.

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All very helpful, folks; much thanks.

Being a geek, I can't help but draw things out; attached is my current plan. I've added blocking underneath where the dogholes will go to provide additional support for the dogs. I was planning on pre-drilling all of them but perhaps will hold off and not drill them until I actually need them. 

Still planning on using 3/4" MDF for the top at this point but may face it with other wood. I did watch John's video on his bench build a bit ago; I'll look at it again.

I haven't included the support needed for the vises. The end vise is on order and I want to have it on hand first. I don't anticipate that being too complicated.

Another noob question: is that too many dogholes? I read somewhere that the spacing between dogholes should be the same as the open limit on the vise. Is that a good rule of thumb to use? 

Any thoughts / feedback on the design would be welcome.

torsion box.pdf

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You say that you are interested in more hand tool work.  Especially with chisel work where you are hitting the chisel with a mallet downward on the bench, a solid surface is much better that a flexible surface so the energy of the mallet all goes into cutting the wood.  You may want to consider solid blocking in that portion of the benchtop where you will be working on you dovetails and other joinery.  I would make a solid wood top.

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On 6/24/2022 at 11:56 AM, John Nalbone said:

Any thoughts / feedback on the design would be welcome.

torsion box.pdf 609.02 kB · 3 downloads

That's a very large benchtop. In a small shop, I wonder if you wouldn't be better off with a smaller workbench for hand tool work and a separate outfeed/assembly table. A torsion box design would be a good choice for the outfeed/assembly table, and maybe a smaller workbench would make solid wood an affordable option. Doesn't need to be fancy wood - Chris Schwarz like Southern Yellow Pine.

If you're wedded to the torsion box design, you might look at this article from Popular Woodworking for some ideas. 

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On 6/23/2022 at 4:36 PM, wtnhighlander said:

Even softer woods like pine or poplar give out quickly under the force applied by a traditionsl hold fast

I can't speak to pine but my poplar work bench dog holes have held up so far for 7 years of hold fast use.  Its made from two 8/4 laminations.

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